M. tuberculosis (TB) is an intracellular parasite that survives in the alveolar macrophage (AM), protected from the immune system. We found that TB induces human AM apoptosis in vitro and apoptosis is a prominent feature of TB granuloma. This suggests that, analogous to Leishmania infection, the AM may destroy itself to deny TB an intracellular sanctuary. Unlike lysis, apoptosis is mycobacterial and limits TB dissemination. Preliminary data shows attenuated strains of TB are more likely to induce apoptosis than virulent strains. This is a novel TB virulence associated phenotype, and suggests that TB-induced apoptosis is a beneficial part of the host response, but these in vitro phenomena have yet to be directly studied in vivo. We have demonstrated apoptosis in murine TB disease. Aim 1 will investigate the in vivo significance and regulation of TB-induced apoptosis in the mouse model of TB disease. Apoptosis in different mouse strains, infected with TB or differing virulence, will be correlated with clinicopathological outcome. Aim 2 will address the mycobacterial molecular basis of TB-induced human macrophage apoptosis. We have already cloned an M. avium DNA fragment that induces macrophage apoptosis. We have already cloned an M. avium DNA fragment that induces macrophage apoptosis. This strategy will be applied to the isolation and characterization of M. tuberculosis and BCG clones that regulate macrophage apoptosis and thus influence virulence. The goals of this K08 application are to acquire conceptual and technical skills in animal TB research, and molecular mycobacteriology through a comprehensive program that includes formal course work, bench research and clinical activities. Collaboration with a center of excellence in animal TB disease (Trudeau Institute) and an apprenticeship in a molecular mycobacteriology lab supplement this learning experience. Participation in national TB meetings and symposia on mycobacterial genetics will be an essential part of the educational plan. This program will provide the education required to become an independent investigator and develop as a clinical scientist. A better understanding of protective response to TB and the virulence factors that control them will contribute to developing new treatments for TB patients and the genetic design of improved vaccines.